Cracking of olefins



States Unite 14 Claims ABSTRACT OF THE DISCLOSURE A promoted pyrolysisprocess is disclosed which comprises providing a mixture of an olefinhaving in its mole cule a carbon-to-carbon single bond which is in aposition beta to the double bond and at least 0.5 and not more than 50mole percent of bromine or a bromine containing compound, subjecting themixture to temperatures ranging from about 500 C. to 900 C. for veryshort periods of time to cleave the carbon-carbon single bond in aposition beta to the double bond of said olefin.

This application is a continuation-in-part of application Ser. No.476,186, filed July 30, 1965, which in turn was a continuation-in-partof application Ser. No. 253,289, filed Jan. 23, 1963, which is acontinuation-in-part of application Ser. No. 802,633, filed Mar. 30,1959, all of which are now abandoned.

This invention relates to the cracking of olefins. More specifically, itrelates to method of improving the cracking of olefins. Mostspecifically, it relates to methods of improving the efiiciency ofcracking of olefins to form specific diolefins and parafiinichydrocarbons or to form certain other specific olefins.

It is known that olefins may be thermally decomposed or cracked bysubjecting them to relatively high temperatures. By the term cracking orcracked as employed throughout this application is meant that the olefinmolecule splits into two fragments. These two fragments themselves formmolecules of other material as explained later. This thermaldecomposition or cracking of olefins is usually conducted within aclosed zone or reactor in the absence of oxygen. Temperatures employedin cracking of olefins usually range from about 300 C. to about 1000 C.Usually olefins are cracked while in a gaseous state and may be fed tothe cracking zone either relatively pure, as mixtures of olefins, inmixture with other hydrocarbons or in mixture with diluents such asnitrogen, steam and the like. The thermal decomposition of olefinsusually results in the formation of a predominance of a diolefin and aparafiinic hydrocarbon and/ or in the formation of a predominance of twoother olefins. The particular materials which predominate when olefinsare cracked depend largely upon the configuration of the olefin which iscracked. By configuration is meant the position of the double bond andthe position of the side chains, if any. For instance, an olefincontaining six carbons with a side chain, i.e. a methyl group attachedto the second carbon atom of the main or straight chain portion of thecompound and the double bond in the 2 position such as 2-methylpentene-2when subjected to cracking will upon decomposition produce as thepredominant products 2-methylbutadiene-1,3 a diolefin, and methane, aparaffin. On the other hand another 6 carbon olefin having a methylgroup attached to the second carbon of the straight chain and the doublebond in the 1 position such as Z-methylatent M 3,529,032 Patented Sept.15, 1970 pentene-l when cracked will produce two other olefins,isobutylene and ethylene. When still another isomer such as4-methylpentene-1 is cracked two mols of propylene are produced. Thesedifferences in products obtained when different isomeric forms ofmethylpentene are cracked are due to the fact that olefins crack at theposition beta to the double bond. That is, the scission occurs at thebond that is in the position beta to the double bond or that the splitoccurs between the two carbon atoms that are second and third removedfrom the carbon atom which is attached to the double bond. Further thesum of the carbon atoms of the main or predominate products of thecracking is equal to the number of carbon atoms contained in the olefinwhich was subjected to the cracking. In 2-methylpentene-2 the crackingremoves only one carbon atom from the 6-carbon olefin, inZ-methylpentene-l two carbon atoms are removed, in 4-methylpentene-lthree carbon atoms are removed because of the location of the betaposition, resulting in the products mentioned above. Thus, theparticular olefin employed usually designates the main or predominantproducts which result from the cracking of olefins.

Employing the most favorable conditions conducive to cracking olefins toform these desired products, it has been found that olefins decompose ata very low rate per pass through the cracking zone. These conditionsbeing temperature, residence time in the zone, and the ratio of theolefin to the gaseous diluent, if any, employed. It is usually thepractice to increase the yield of decomposition of olefins and of thedesired end products by separating the unreacted or undecomposed olefinfrom the products resulting from the cracking and returning or recyclingthe unreacted olefin to the cracking zone. Usually, however, regardlessof how many recycles are carried out the ultimate yield or ultimatedecomposition of the olefin is not greater than about 60 mol percent ofthe olefin being converted or decomposed to the desired products, theremaining 40% being converted to undesirable products as the result ofside reactions caused by high temperature or long residence times in thecracking zone.

It is, therefore, the main object of this invention to provide a methodwhereby the yield of the desired products produced by cracking olefinsis increased. Another object is to provide a method whereby the crackingof olefins to desired products per pass is increased. Another object isto increase the ultimate yield of desired products from the crackingolefins. Another object is to provide a method whereby the residencetime of cracking of olefins may be decreased. Another object is toprovide a method whereby the promotion of undesirable side reactionsduring the cracking of olefins is decreased. Another object is toprovide a method whereby olefins may be cracked at lower temperatures.Another object is to provide a promoter for the cracking of olefins tothe desired products. Still another object is to provide a methodwhereby the size of equipment needed to crack a certain volume ofolefins is reduced.

The objects of this invention are accomplished by cracking olefins inthe presence of bromine.

In general, the cracking of olefins in accordance with the practice ofthis invention may be carried out in any conventional manner usuallyemployed in the art of cracking olefins.

Generally, the conditions of cracking may be widely varied, dependingupon the particular olefin to be cracked and the products desired. Forinstance, the temperature of cracking may be varied from about 300 C. toabout 1000 C. However, it is usually preferred to crack olefins attemperatures ranging between 500 and 900 C. and it is generally mostpreferred to employ temperatures ranging between 600 and 700 C.

The time that the olefins are in the cracking zone during the practiceof this invention may range broadly from about 0.001 to about 3 seconds.However, it is preferable that times varying from 0.05 to 0.5 second beemployed. These times are referred to usually as residence times and areusually defined as the time required for one mol of incoming gas, be itpure olefin or mixtures with other ole fins or diluents, to pass throughthe cracking zone. The rate of feed of olefins to the cracking zone maalso be expressed in another term called space velocity. Space velocityis reported in units of volume of gas/volume of reactor space/hour andis usually called gaseous hourly space velocity (GHSV). Space velocityemployed in cracking of olefins in the practice of this invention mayrange broadly from 3,600,000 to 1200 GHSV. However, it is generallypreferred to employ space velocity ranging from about 72,000 to 7200GHSV. Thus, the space velocity is inversely proportional to theresidence time.

Generally, the olefins are fed to the cracking reactor either as pureolefins or in mixture with other olefins or in mixture with some inertdiluent. By the term inert diluent is meant that the diluent does not inany way affect the cracking of the olefin and has no effect upon theproducts formed in the cracking operation. it is usually desirable toemploy a diluent such as steam, carbon dioxide, hydrogen or parafiinssuch as methane, ethane, propane, butanes, pentanes, and olefins such asethylene. These hydrocarbons do not crack at the temperatures employedto crack the olefins in the practice of this invention. Of these, steamis preferred because of economy and because it suppresses the formationof coking and aids in the removal of coke via the reaction H Q+C=H +COif coke is formed. Propane and pentane are also preferred.

The ratio of diluent to olefin employed in the practice of thisinvention may be widely varied from about 0.5/ l to about 15/ 1 or moremols of diluent per mol of olefin. However, if more than about a 15/1ratio is employed the process is no longer economical. It is preferredto use a diluent to olefin ratio ranging from about 2.0/1 to 4.0/ 1.

The pressures employed in the cracking zone while cracking olefins maybe varied from about 10 millimeters of mercury to 500 pounds per squareinch gauge. However, it is preferred that the pressure range from about"atmospheric to about 35 pounds per square inch gauge.

The bromine (Br) employed in the practice of this invention may be usedin amounts varying from about 0.5 to about 50 mol percent of brominebased on the total mols of the olefin to be cracked. A more preferredrange of bromine is from about 1.5 to about 40 mol percent. Still a morepreferred range varies from about 2.5 to about 25 mol percent. It hasbeen found, however, that excellent results have been obtained byemploying from about 5 to about mol percent of bromine.

The bromine employed to increase the efficiency of the cracking ofolefins in accordance with the practice of this invention may besupplied either in the gaseous form or as a liquid under pressure. Inaddition to bromine itself, any organic or inorganic bromine-liberatingcompound, i.e. an organic or inorganic bromine-containing compound whichdecomposes under the conditions of cracking employed to produce bromine,may also be employed to accomplish the purposes of this invention. Iforganic bromine-liberating compounds are to be employed, it has beenfound convenient to use them in the form of a solution by dissolvingthem in the olefin to be cracked. If an inorganic bromine-liberatingcompound is to be employed, it has been found convenient to dissolve theinorganic bromine in water which is later converted to steam and as suchforms the inert cracking diluent. Representative examples of the organicbromides which have been successfully employed in the practice of thisinvention are ethyl bromide, 2-bromopropane, l-bro-mobutane,

1 bromopropane, a bromo toluene, bromobenzene, bromochloro methane,1,2-dibromoethane and the like. Representative examples of the inorganicbromides which have been successfully employed in the practice of thisinvention are hydrogen bromide and a water-soluble bromine salt such asNH Br. Of these it is preferred to employ NI-LLB].- and hydrogenbromide.

If the promoter is a compound which produces hydrogen bromide under thecracking conditions employed or is the preferred embodiment, hydrogenbromide or NH Br, the amounts may vary broadly from about 0.5 to about50 mol percent based on the total mols of olefin to be cracked. A morepreferred range of hydrogen bromide is from about 0.5 to about 25 molpercent. Still a more preferred range varies from about 0.5 to about 10mol percent. Best results are usually obtained by employing from about1.5 to about 5 mol percent of hydrogen bromide based on the mols ofolefin to be cracked.

All the compounds useful in the practice of this invention must eitherdecompose or dissociate to form bromine in the form of Br. Even bromine(Brgas at the temperatures employed dissociates to the form Br. However,when the bromine passes from the cracking zone to Where it is recoveredit is in the form HBr regardless of form in which it was introduced.Since HBr is a preferred form of introducing bromine in the practice ofthis invention and is soluble in water, a very good and economicalembodiment of this invention is to employ HBr as the bromine producingagent and steam as the cracking diluent thereby providing a solution ofHBr in water which can be recovered and recycled over and over again.

The practice of this invention is illustrated by the followingexperiments which are to be interpreted as representative rather thanrestrictive of the scope of this invention. The results and conditionsof the cracking experiments are reported in table form.

All of the cracking experiments were performed in a reactor assemblyconsisting of a hairpin coil prepared from A-inch OD 316 stainless steeltubing. This coil reactor was immersed in a bed of fluidized heattransfer powder which was microspheroidal silica-alumina crackingcatalyst. The heat transfer powder was heated both by electricalresistance heaters and by combustinig a natural gas flame in thefluidized powder bed. The temperature gradient from top to bottom of thebed was never more than 5 to 6 C. and the gradient from the fluidizedbed to the tube walls Was about 56 C. The temperatures within thefluidized bed were measured by conventional thermocouple techniques asWere the temperatures Within the cracking zone. The procedure employedwas to bring the heat transfer powder up to about 500 C. employing theelectrical resistance heaters While fluidizing the heat transfer powderwith air. Then the natural gas burner was employed to bring the heattransfer powder up to the desired cracking or operating temperature. Thebromine vvas supplied in the form of a bromine-liberating compound whichat the cracking temperatures dissociated to produce bromine as Br; acalculated amount of the compound was dissolved in either the olefins orthe Water, depending on the particular compound employed, to give thedesired amount of bromine (Br) required in each experiment. The Waterand the olefin were pumped at the proper rates necessary to produce theH O/hydrocarbon ratio desired and to give the desired residence time ofthe materials in the cracking zone or cracking reactor. When allvariables had been adjustated to give the desired operating conditionsthe product of the cracking were col lected if liquid by means of cooledreceivers and if gas were metered at atmospheric and room temperatureconditions. The products were analyzed for content and yields byconventional analytical methods. Conventional recycle techniques wereemployed to obtain the ultimate yield.

The results of each experiment as Well as operating conditions arereported in the tables below wherein column one is the experimentnumber, column two is the actual cracking temperature, column three isthe residence time in seconds, column four is the ratio ofdiluent/hydrocarbon, column five is the mol percent of bromine as Br Thepressure employed in these experiments was 0.97 pound per square inchgauge. Steam was employed as the diluent.

Resi- M01 percent Percent Experl- Temp, dence Ratio M01 percent isopreneefficiency to ment 0. time HzO/HC HBr yield isoprene 674. 6 0. 4410 4.12 5. 50 54. 76 61. 90 672. 5 O. 2070 4. 22 4. 29 41. 95 66. 65 663. 40. 5410 5. 01 None 23. 68 52. 96 660. 5 0. 5550 4. 98 None 25. 03 57. 20

regardless of the compound from whence it came based on the mols ofolefin charged, unless otherwise noted, column six is the yield ofdesired product reported in mol percent per mol of olefin charged, andcolumn seven is the ultimate yield also called efliciency of the desiredproduct obtained by employing recycle techniques.

EXPERIMENTS 1-6 Decomposition of 2-methylpentene-2 to isoprene In theseexperiments hydrogen bromide was employed as the bromine-producingcompound. Experiments 2, 4 and 6 were considered controls and do notcontain any EXPERIMENTS 15-23 Decomposition of 2-methylpentene-2 toisoprene M01 Percent percent efliciency Temp, Resldence Ratio Bromineisoprene to Experiment 0. time H/HC compound yield isoprene 15 642. 0 0.1904 3. 16 Ethyl bromide 27. 27 36. 75 16 653. 3 0. 2803 2. 96 2-bromo-35. 38 54. 76

propane. 17 656. 0 0. 2117 2. l-bromo- 36. 96 51. 02

butane. 18 654. 7 0. 2187 2. 86 l-bromo- 34. 67 46. 60

propane. 19 649. 0 0. 2406 2. 92 ot-BYODIIO- 25. O6 32. 12

toluene. 20 647. 9 0. 2437 2. 60 Bromo- 17. 24 45. 60

benzene. 21 649. 2 0. 2287 2. 76 Bromo-chloro- 27. 36 41. 15

methane. 655. 1 0. 2206 2. 66 1,2-di-bromo- 33. 05 44. 02

ethane. 656. 0 O. 2109 2. 80 None 13. 49 39. 80

bromine. The pressure employed in the cracking of these experiments wasabout 0.98 pounds per square inch absolute. Steam was used as thediluent.

Thus it can be observed from the foregoing experiments that the use ofbromine in the cracking of these particular olefins results in astriking increase in the Resl- M01 percent Percent Temp., dence RatioM01 percent isoprene efficiency to 0. time HgO/HO HBr yield isoprene576. 0 0. 46 3. 18 3. 16 8. 00 55. 00 575. 0 0. 50 3. 25 None 6. 00 40.50 600.0 0.53 2. 53 2. 52 17. 72 58. 68 602. 3 0. 57 4. 00 None 8. 3839. 09 626. 0 0. 50 2. 90 2. 89 30. 46 57. 75 626. 7 0. 54 4. 00 None12. 98 49. 40

EXPERIMENTS 7-10 Decomposition of 2-methylpentene-2 to isoprene In theseexperiments hydrogen bromide was employed 55 as the bromine-producingcompound and is reported as mol percent hydrogen bromide per mol ofolefin charged. Experiments 7 and 10 are considered controls and do notcontain any bromine. The pressure employed in the cracking in theseexperiments was about 0.97 pound per square inch gauge. Steam was usedas the diluent:

Resi- Mo1 percent Percent Experi- Temp., dence Ratio M01 percentisoprene efificiency to ment 0. time HzO/HC HBr yield isoprene 651. 0 0.2028 5. 59 None 10. 97 51. 11

677. 4 0. 2070 6. 15 None 21. 15 41. 50

EXPERIMENTS 11-14 Decomposition of 3-methylpentene-2 to isoprene inbromine is employed in the remaining experiments there is illustratedthat a very definite advantage is obtained either in the increase of thedesired product per pass or in increase in the ultimate yield whenolefins are cracked.

Similar results may be obtained employing the general techniquesemployed in examples above wherein the fol- In these experimentshydrogen bromide was used as the bromine-producing compounds and isreported as mol percent HBr per mol of olefin. Experiments 13 and 14 areconsidered controls and do not contain any bromine.

lowing representative olefins may be cracked in accordance with thepractice of this invention. These olefins are listed in groups whichwill crack to produce predominatly one desired diolefin or one desiredolefin.

Representative of the olefins that will decompose to form as a majorproduct 2-methylpentadiene-1,3 and 4- ployed to produce iodine andchlorine. The conditions employed were similar and the results andconditions are listed below. Experiment 24 is considered as the controland does not contain any iodine, chlorine or bromine. Experiments 25 and26 contain chlorine and 27-30 contain iodine.

methylpentadiene-1,3 are: 2-methylhexene-3; Z-ethylpentene-l;2,4-dimethylpentene-2; 2-methylheptene-3; 4,4- dimethylhexene-Z;2-propylpentene-2 and 2,6-dimethylheptene-3. Of these 2-methylheXene-3,and 2,4-dimethylpentene-2 are preferred.

Representative of the olefins which will decompose to form as a majorproduct 3-methylpentadiene-l,3 are 3- methylhexene-3; 3-methylheptene-3;3,4-dimethylhexene- 2; 3,6-dimethylheptene-3. Of these 3-methylhexene-3;3-methylheptene-3 and 3,4-dimethylhexene-2 are preferred.

Representative of the olefins which decompose to form as a major product2,3-dimethyl butadiene-l,3 are: 2,3- dimethylpentene-Z;2,3,3-trimethylbutene-l; Z-isopropylpentene-l; 2,3,3-trimethylpentene-1;2,3-dimethylheptene- 2; and 2,3-dimethylhexene-2. Of these2,3-dimethylpentene-2; 2,3,3-trimethylbutene-l;2,3,3-trimethylpentene-l; 2,3-dimethylhexene-2 and 2,3-dimethylpentene-1are preferred.

Representative of the olefins which decompose to form as a major product2-ethy1 butadiene-1,3 are: 3-ethylpentene-2; and 3-ethylhexene-2. Ofthese 3-ethylpentene-2 and 3-ethylheXene-2 are preferred.

Representative of the olfins which will decompose to form as a majorproduct butadiene-l,3 are: pentene-Z; hexene-2; 3-methylpentene-l;cyclohexene; 3-methylbutene-l; Z-heptene; 3-methylhexene-1;S-methylhexene-Z; 2-octene; -methylheptene-2; 3,5-dimethylhexene-l;3,4,4- trimethylpentene-l; 6-methylheptene-2; nonene-2; and 3-methyloctene-l. Of these pentene-2; hexene-Z; heptene-2 and cyclohexeneare preferred.

Representative of the olefins which will decompose to form as a majorproduct isoprene are: 2-methylpentene-2; 3-methylpentene-2;Z-ethylbutene-l; 3,3-dimethylbutene-l; 2,3-dimethylbutene-l;2-methylhexene-2; 3-methylhexene- 2; 2,3-dimethylpentene-1;3,3-dimethylpentene-1; 2- methylheptene-2; 3-methylheptene-2;2-ethylhexene-l; 3,3- dimethylhexene-l; 2,5-dimethylhexene-2;3,5-dimethylheXene-2; 2,3-dimethylpentene-1 and 3,3-dimethylpentene- 1.Of these, Z-methylpentene-Z; 3-methyl-pentene-2; 2- ethylbutene-l;2,3-dimethylbutene-1; 3,3-dimethylbutene- 1; 2-methylhexene-2;3-methylhexene-2; 2,3-dimethylpentene-l and 3,3-dimethylpentene-1 arepreferred.

Representative of the olefins that will decompose to form as a majorproduct piperylenes are: hexene-3; 4- methylpentene-Z; heptene-3;4-methylheXene-2; octene-3; 4-methylheptene-2; 3-ethylhexene-1;4,5-dimethylheptene 2; and 4,5,5-trimethylhexene-2. Of these hexene-3;4- methylpentene-2 and heptene-3 are preferred.

The following experiments were performed to illustrate that theimprovements gained by the practice of this invention are peculiar tobromine alone and not to halogens in general.

EXPERIMENTS 24-30 Decomposition of 2-methylpentene-2 In theseexperiments the olefin 2-methylpentene-2 Were cracked in a mannersimilar to the prior experiments except hydrogen iodide and hydrogenchloride were em- Thus it is noted that by employing iodine and chlorinewhile cracking olefins instead of any improvement being obtained, thereis a detrimental effect obtained. In all cases poorer yields areobtained than was obtained in the control experiments.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in this art that various changes and modifications may be madetherein without departing from the spirit or scope of the invention.

What is claimed is:

1. A promoted pyrolysis process which comprises providing a mixture ofat least one olefin having in its molecule a carbon-to-carbon singlebond which is in a position beta to the double bond and selected fromthe group consisting of 2-methylhexane-3, Z-ethyIpentene-l, 2,4-dimethylpentene 2, 2 methylheptene-3, 4,4-dimethy1- hexene 2, 2propylpentene-2, 2,6-dimethylheptene-3, 3 methylhexene 3, 3methylheptene-3, 3,4-dimcthylhexene 2, 3,6 dimethylheptene-3,2,3-dimethylpentene- 2, 2,3,3 trimethylbutene 1, 2-isopropy1pentene-1,2,3,3- trimethylpentene 1, 2,3 dimethylheptene 2, 2,3-dimethylhexene 2,3 ethylpentene 2, 3-ethylhexene 2, pentene 2, hexene 2, 3 methylpentene1, cyclohexene, 3 methylbutene 1, 2 heptene, 3 methylhexene 1, 5-methylhexene 2, 2 octene, 5 methylheptene 2, 3,5- dimethylhexene 1,3,4,4 trimethylpentene 1, 6-methy1- heptene 2, nonene 2, 3 methyloctene1, 2 methylpentene 2, 3 methylpentene 2, 2 ethylbutene 1, 3,3-dimethylbutene 1, 2,3 dimethylbutene 1, Z-methylhexene 2, 3 methylhexene2, 2-methy1heptene-2, 3- methylheptene 2, 2 ethylhexene 1, 3,3dimethylhexene 1, 2,5 dimethylhexene 2, 3,5 dimethylhexene 2, 2,3dimethylpentene 1, 3,3 dimethylpentene 1, hexene 3, 4 methylpentene 2,heptene 3, 4methylhexene 2, octene 3, 4 methylheptene-2,3-ethylhexene-1, 4,5 dimethylheptene 2 and 4,5,5-trimethylheXene-2 and acracking promoter comprising at least 0.5 mole percent and not more than50 mole percent, based on the moles of said olefin in said mixture ofbromine, cleaving the carbon-to-carbon single bond which is in aposition beta to the double bond of said olefins, by subjecting said mixture to temperatures ranging from about 500 C. to about 900 C. forperiods of time varying from about 0.05 to about 0.5 second.

2. A process according to claim 1 in which the olefin pyrolyzed is atleast one selected from the group consisting of Z-methyl pentene-2;3-methyl pentene-2; 2-ethyl butene-l; 3,3-dimethylbutene-1; 2,3-dimethylbutene-l; 2- methyl hexene-2; 3-methyl hexene-2; 3,3-dimethyl pentene-l;and 2,3-dimethyl pentene-l and in which isoprene is prepared as themajor product.

3. A process according to claim 1 in which the olefin to be pyrolyzed isat least one selected from the group consisting of 3-ethyl pentene-2 and3-ethyl hexene-2 and in which 2-ethyl butadiene-l,3 is prepared as themajor product.

4. A process according to claim 1 in whch the olefin to be pyrolyzed isat least one selected from the group consisting of pentene-2; hexene-Z;3-methyl butene-l; heptene-Z; and cyclohexene and in which butadiene-1,3is prepared as the major product.

5. A process according to claim 1 in which the olefin to be pyrolyzed isat least one selected from the group consisting of 2,3-dimethy1pentene-Z; 2,3,3-trimethyl butene-l; 2,3,3-trimethyl pentene-l; and2,3-dimethyl hexene-2 and in which 2,3-dimethyl butadiene-l,3 isprepared as the major product.

6. A process according to claim 1 in which the olefin pyrolyzed is atleast one selected from the group consisting of hexene-3; 4-methy1pentene-2; heptene-3; and 4-methy1 hexene-Z and in which piperylene isprepared as the major product.

7. A process according to claim 1 in which the olefin pyrolyzed is atleast one selected from the group consisting of 3-methy1 hexene-3;3-methy1 heptene-S; and 3,4-dimethyl hexene-Z and in which 3-methylpentadiene-l,3 is prepared as the major product.

8. A process according to c aim 1 in which the olefin pyrolyzed is atleast one selected from the group consisting of 2,4-dimethyl pentene-2;Z-methyl heptene-3; 4,4-dimethyl hexene-Z; and 2-propyl pentene-Z and inwhich 2- methyl pentadiene-1,3 and 4-methy1 pentadiene-l,3 are preparedas the major products.

9. A method according to claim 1 in which the bromine is provided bymeans of hydrogen bromide.

10. A method according to claim 2 in which the bromine is provided bymeans of hydrogen bromide.

11. A method according to claim 1 in which the bromine is provided bymeans of ammonium bromide.

12. A process according to claim 2 in which bromine is provided by meansof ammonium bromide.

13. A process according to claim 2 in which the olefin to be pyrolyzedis Z-methyl pentene-Z and the bromine is provided by means of ammoniumbromide.

14. A process according to claim 2 in which the olefin to be pyrolyzedis 3-methyl pentene-2 and the bromine is provided by means of ammoniumbromide.

References Cited UNITED STATES PATENTS 1,880,310 10/1932 Wullf 2606792,370,513 2/1945 Amos et a1. 260680 2,397,638 4/1946 Bell et a1. 2606832,402,034 6/1946 Folkins et a1. 260683 2,404,056 7/1946 Gorin et a1.260680 2,423,494 7/1947 Folkins et a1. 260683 3,104,269 9/1963 Schaffel260680 3,250,821 5/ 1966 Bullard 260680 FOREIGN PATENTS 807,149 1/1959Great Britain. 831,249 3/ 1960 Great Britain. 1,275,949 10/ 1961 France.

247,253 9/1963 Australia.

PAUL M. COUGHLAN, 111., Primary Examiner US. Cl. X.R. 260--683

